But the 1st District has historically been considered a blue district. Registered Democrats there continue to outnumber registered Republicans by about 17,000 people.

Wasserman said both Democrats will need to step up their fundraising game as the race continues. Blum, as an incumbent, has considerably more cash on hand and than either of his challengers, reporting $883,779 at the end of the last quarter.

Finkenauer has $168,586 in cash on hand, and Heckroth reported $105,295.

"The fundraising quarters that Finkenauer and Heckroth turned in were respectable but not magnificent," Wasserman said. "They’re, I would say, not earth shattering. They’ll need to raise more money to keep up with the incumbent as the cycle progresses."

Finkenauer, 28, from Dubuque, is in her second term as a state representative and serves on the board of the Greater Dubuque Development Corporation. She hails from a union household and has gained endorsements from EMILY's List, NARAL Pro-Choice America and several Iowa labor unions.

Heckroth, 33, from Cedar Rapids, previously worked for former U.S. Sen. Tom Harkin, D-Iowa, and in the U.S. Department of Labor under President Barack Obama's administration. Later, he and his wife moved to New York, where he oversaw sustainable manufacturing and sourcing for a children’s clothing maker for Nike and Levi’s.

Two other Democrats have filed in the race: George Ramsey, an army veteran from Cedar Rapids, reported $358 in cash on hand, and Courtney Rowe, an aeronautical engineer from Cedar Rapids, reported $1,509 in cash on hand.

Campaign fundraising

Here's a look at how much candidates across the state reported in cash on hand for the quarter that ended Sept. 30. Those federal financial reports were due Oct. 15, though some were not yet available online. Senate candidates file their financial reports differently and are not immediately available after the filing deadline.

1st District

Rod Blum, Republican incumbent: $883,779.07

Abby Finkenauer, Democrat: 168,586.28

Thomas Heckroth, Democrat: $105,295.85

George Ramsey, Democrat: $358.81

Courtney Rowe, Democrat: $1,509.53

2nd District

Dave Loebsack, Democrat incumbent: $1,499,465.39

Chris Peters, Republican: $26,169.10

3rd District

David Young, Republican incumbent: $626,704.49

Cynthia Axne, Democrat: $104,642

Austin Frerick, Democrat: $5,429.02

Paul Knupp, Democrat: $2,237.99

Eddie Mauro, Democrat: $161,899

Heather Ryan, Democrat: N/A

Theresa Greenfield, Democrat: $147,651.61

Pete D’Alessandro, Democrat: $26,621.56

4th District

Steve King, Republican incumbent: N/A

Paul Dahl, Democrat: N/A

Leann Jacobsen, Democrat: $38,202.57

John Paschen, Democrat: $11,896.07

J.D. Scholten, Democrat: $7,592.98

Editor's Note: This article was updated Oct. 17, 2017 to include newly available financial information for Cindy Axne and Eddie Mauro.